The present invention relates to an apparatus and method for decontaminating a radioactive metallic waste for the purpose of reducing the radioactivity occurring during operation, outage for inspection and decommission of the nuclear facilities and included in a metallic waste, and more specifically, to an apparatus and method for decontaminating a radioactive metallic waste for the purpose of reducing the radioactivity included in metallic waste having shapes of a pipe, plate and the like.
Various methods are provided for completely decontaminating the radioactivity included in a radioactive metallic waste and occurring during operation of the nuclear power establishment, at an outage for inspection of the nuclear facilities and at decommissioning the waste. For example, Japanese Patent Laid-open No. 62-46297 and No. 60-186799 disclose an electrolysis decontamination using acid and neutral salt (chloride) solution, which have been developed and utilized.
The electrolysis decontamination is effective with respect to the metallic waste having a comparatively simple shape such as a plate, a cylindrical object and the like. A system of the electrolysis decontamination, comprises an anode as a metallic waste, and a cathode arranged in front of a surface to be decontaminated on the metallic waste as the anode, in which a direct voltage is supplied between the metallic waste (anode) and the cathode to polish a base metal on the surface to be decontaminated, thereby decontaminating the radioactivity from the metallic waste.
The electrolysis. decontamination mentioned above, however, has the problems as follows:
i) Since the contamination remains behind a connection portion between the metallic waste and the anode because the connection portion is not dissolved, it is necessary to change the manner of holding the anode to decontaminate again so as to complicate the decontamination; PA1 ii) When large scale device and apparatus are decontaminated, since a current value becomes large in proportion to a surface area, it is necessary to provide an anode clamper under the consideration of a contact area. Accordingly, it is also necessary to frequently change the anode clamper to match the shape with the device and apparatus; and PA1 iii) When large number of device and apparatus are treated, since it is necessary to change the manner of holding the anode and to change the anode clamper, it is possible for an operator to receive an increased exposure. PA1 an electrolysis bath having a predetermined shape and filled up by an electrolyte which has predetermined component, density and temperature for performing the electrolysis; PA1 an anode arranged in the electrolysis bath with a predetermined shape and charged in a positive polar by a direct current (DC) voltage supplied from a DC power source; and PA1 a cathode arranged in the electrolysis bath with a predetermined shape and charged in a negative polar by the DC voltage supplied from the DC power source: PA1 wherein the predetermined shape of at least any of electrodes of the anode and cathode is formed in correspondence with the predetermined shape of the metallic waste which is set in the electrolysis bath. PA1 an insulating shield plate for dividing a room of the electrolysis bath into an anode chamber and a cathode chamber, and the insulating shield plate which is set in a U-shape along three inner wall surfaces of the electrolysis bath. PA1 the insulating shield plate is a vessel having an opening at an upper portion thereof; PA1 the anode is arranged at a bottom portion of the electrolysis bath; PA1 the cathode is arranged at a bottom portion of the electrolysis bath; PA1 the metallic waste is supported by an insulation supporting member; and PA1 the insulation supporting member is arranged at the bottom of the electrolysis bath having the opening at the upper portion and has a plurality of holes each of which opens in a mesh-shape for passing through the electrolyte. PA1 the insulation supporting member is comprised of a basket which has an opening at an upper portion thereof, and stores the metallic waste therein. PA1 the cathode is comprised of a rectangular pipe or a bar-shaped body, and moves with keeping a constant interval against the metallic waste by a driving mechanism. PA1 the cathode is comprised of a blind cathode which is formed by connecting a plurality of rectangular pipes or bar-shaped bodies by a flexible cable, the blind cathode which has an insulating elastic body for allowing a water passing therethrough. PA1 any one of electrodes of two kinds of the anode and the cathode for electrolysis has a cylindrical shape along the outer shape of the metallic waste having a curved portion, and the other of the electrodes is formed in a bar-shape in correspondence with an inner shape of the metallic waste. PA1 an electrolysis bath; PA1 a cylindrical anode which is arranged in the electrolyte in the electrolysis bath; PA1 a cylindrical metallic waste which is arranged in the cylindrical anode; PA1 a bar-shape cathode which is arranged in the cylindrical metallic waste; and PA1 a direct current power source for connecting the cylindrical anode and the bar-shape cathode. PA1 an electrolysis bath; PA1 a cylindrical insulating shield body which is arranged in the electrolyte in the electrolysis bath; PA1 a cylindrical anode which is arranged on an inner wall of the cylindrical insulating shield body; PA1 a cylindrical cathode which is arranged on an outer wall of the cylindrical insulating shield body; PA1 a cylindrical metallic waste which is arranged in the cylindrical anode; and PA1 a direct current power source for connecting the cylindrical anode and the bar-shape cathode. PA1 insulating discs each having an opening are arranged at the upper and lower ends of the cylindrical insulating shield body. PA1 an electrolysis bath; PA1 an insulating shield vessel which is arranged in the electrolysis bath and has an opening at the upper portion thereof; PA1 a cathode which is arranged at the bottom of the electrolysis bath; PA1 an anode which is arranged at the bottom of the insulating shield vessel; PA1 a supporting vessel which is arranged in the insulating shield vessel to keep a metallic waste and has an opening at the upper portion thereof: wherein PA1 the supporting vessel has a side surface formed of insulating material, and a bottom portion formed of metal material, and PA1 the side surface of the supporting vessel has a plurality of holes for allowing the electrolyte therethrough. PA1 an electric circuit is configured in the manner that the DC voltage is supplied between the anode and the cathode for charging in a negative polarity metal material at the bottom portion of the supporting vessel facing to the anode, and for charging in a positive polarity an upper surface of the metallic waste kept by the supporting vessel. PA1 a step of filling up the electrolyte having predetermined component, density and temperature into an electrolysis bath having a predetermined shape for performing the electrolysis; PA1 a step of setting the metallic waste at a predetermined position between a pair of electrodes including an anode and cathode and corresponding to the shape of the metallic waste; and PA1 a step of supplying a direct current (DC) voltage from a DC power source to the pair of electrodes to charge in a positive polarity any one of the pair of electrodes to be the anode and to charge in a negative polarity the other of the pair of electrodes to be the cathode for performing the electrolyte, thereby dissolving the base metal of the metallic waste. PA1 a step of dividing a room in the electrolysis bath into an insulating shield plate into an anode chamber and a cathode chamber; PA1 a step of setting an anode in the anode chamber; PA1 a step of setting a cathode and the metallic waste in the cathode chamber; PA1 a step of supplying the DC voltage to the anode and cathode from the DC power source connected to the anode and cathode, respectively; and PA1 a step of charging in a positive polar to a decontamination surface of the metallic waste facing to the cathode. PA1 when entire of both surfaces of the metallic waste are contaminated by the radioactivity, a polarity of the DC power source is converted to change the anode to a cathode and the cathode to an anode so as to dissolve the other surface of the metallic waste. PA1 a step of using inorganic acid as the electrolyte; PA1 a step of supplying the DC voltage to the pair of electrodes; PA1 a step of reducing and destroying a passive or oxide layer on the predetermined surface of the metallic waste facing to the cathode by charging in a negative polar to the other surface of the predetermined surface; and PA1 a step of stopping a supply of the DC voltage and dissolving the base metal of the metallic waste by using acid force of the inorganic acid. PA1 a dissolution of the base metal and a reduction and destruction of the passive or oxide layer are repeated by alternatively inverting a polarity of the DC power source. PA1 a step of setting a cylindrical anode in the electrolyte; PA1 a step of setting a cylindrical metallic waste in the cylindrical anode; PA1 a step of setting a bar-shape cathode in the cylindrical metallic waste; PA1 a step of supplying the DC voltage from the DC power source to a portion between the cylindrical anode and the bar-shape cathode; and PA1 a step of charging in a positive polar to an inner surface of the cylindrical metallic waste and in negative polar to an outer surface of the cylindrical metallic waste, thereby dissolving the inner surface of a base metal of the metallic waste. PA1 when both of the inner surface and the outer surface of the cylindrical metallic waste are contaminated, a cathode of the DC power source is inverted to an anode, and an anode of the DC power source is inverted to a cathode, thereby dissolving the outer surface of the cylindrical metallic waste. PA1 a dissolution of the base metal of the inner surface of the cylindrical metallic waste and a reduction and destruction of the oxide layer formed on the inner surface of the cylindrical metallic waste are repeated by alternatively inverting a polarity of the DC power source. PA1 a step of setting a cylindrical insulating shield body in the electrolyte; PA1 a step of setting a cylindrical anode on an inner wall of the cylindrical insulating shield body, PA1 a step of setting a cylindrical cathode on an outer wall of the cylindrical insulating shield body; PA1 a step of setting a cylindrical metallic waste in the cylindrical anode; PA1 a step of connecting the DC power source to the cylindrical anode and the cylindrical cathode; PA1 a step of supplying the DC voltage from the DC power source to the cylindrical anode and cylindrical cathode; and PA1 a step of charging in a negative polarity an outer surface of the cylindrical metallic waste and in a positive polarity an inner surface of the cylindrical metallic waste, thereby dissolving a base metal at an inner surface of the cylindrical metallic waste. PA1 when both of the inner surface and the outer surface of the cylindrical metallic waste are contaminated, a cathode of the DC power source is inverted to an anode, and an anode of the DC power source is inverted to a cathode, thereby dissolving the outer surface of the cylindrical metallic waste. PA1 a dissolution of the base metal of the inner surface of the cylindrical metallic waste and a reduction and destruction of the oxide layer formed on the inner surface of the cylindrical metallic waste are repeated by alternatively inverting a polarity of the DC power source.
A related patent application has been filed at the JPO as Japanese patent application laid-open No. 5-297192, and No. 6-242295 for decontaminating the radioactivity of the metallic waste by using a bipolar electrolytic with non-contact. The present invention provides higher function and high performance than the previous methods.